Before the external debugger can use any of the access ports, the debugger must first request the device to power up via CxxxPWRUPREQ in the SWJ-DP.
As long as the debugger is requesting power via CxxxPWRUPREQ, the device will be in Debug interface mode. Otherwise, the device is in Normal mode. When a debug session is over, the external debugger must return the device back to Normal mode and perform a pin reset. This is due to the overall power consumption being higher in Debug interface mode compared to Normal mode.
Some peripherals behave differently in Debug interface mode compared to Normal mode. These differences are described in more detail in the chapters of the affected peripherals.
For details on how to use the debug capabilities, read the debug documentation of your IDE.
If the device is in System OFF when power is requested via CxxxPWRUPREQ, the device will wake up and the DIF flag in RESETREAS will be set.